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Re: debian-installer: please default to grub-ieee1275 on powerpc instead

From: John Paul Adrian Glaubitz
Subject: Re: debian-installer: please default to grub-ieee1275 on powerpc instead of yaboot
Date: Thu, 21 Sep 2017 22:37:43 +0200
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On 09/21/2017 07:02 PM, Lennart Sorensen wrote:
> On Thu, Sep 21, 2017 at 06:26:10PM +0200, John Paul Adrian Glaubitz wrote:
>> Ok, good to know. What about GPT partition tables? On ppc64el, i.e. POWER8
>> and newer, the default labels are all GPT. Any idea which is the earliest
>> POWER5+ machine which supports GPT or should we just assume MS-DOS
>> partition tabels for all POWER machines?
> I unfortunately never tried GPT on any IBM power machines and I no longer
> have access to them.

I have one POWER7 machine that has been provided to me by IBM for testing
purposes and to host one of our buildds. I have performed a test installation
of openSUSE Tumbleweed on it.

Here's the partitioning scheme that is being used:

(parted) p
Model: Virtio Block Device (virtblk)
Disk /dev/vda: 42.9GB
Sector size (logical/physical): 512B/512B
Partition Table: msdos
Disk Flags:

Number  Start   End     Size    Type     File system     Flags
 1      1049kB  2097kB  1049kB  primary                  boot, prep, type=41
 2      2097kB  2163MB  2161MB  primary  linux-swap(v1)  type=82
 3      2163MB  18.9GB  16.7GB  primary  btrfs           type=83
 4      18.9GB  42.9GB  24.0GB  primary  xfs             type=83


Interestingly, /boot is part of the btrfs filesystem:

linux-mfl2:~ # mount | grep boot
/dev/vda3 on /boot/grub2/powerpc-ieee1275 type btrfs 
linux-mfl2:~ #

> I found this:
> So it claims that on power7 the firmware upgrade in 2013 added support
> for booting from a GPT disk.  So to me that means a lot of power7 systems
> out there won't be able to (since not everyone has updated the firmware).
> It doesn't say what you have to create as a boot partition when using
> GPT though, so no idea how one would use it.  It might support FAT32
> filesystem and accessing the grub file the way UEFI systems do, and
> similar to what I think PowerMac machines do.
> I can't find anything to suggest any power6 or power5 system ever had
> an update to allow it.

Ok, so I guess we can basically rule out GPT for the default label even
on POWER systems. I would therefore then vote for using MS-DOS partition
tables on POWER systems, i.e. what is already used now.

> I would expect all power8 machines had GPT support from the start,
> and hence defaulting to that makes sense.

I agree.

>>> The grub modules stay in whatever /boot is on, and the grub image
>>> generated contains enough of grub to read filesystems and is loaded
>>> by the firmware from the prep boot partition (it litterally reads that
>>> partition into ram as raw data, and executes it). 
>> Interesting. Do you know whether the mechanism is the same? My worries
>> are that users on older PowerPC hardware, especially Apple Macintosh
>> would have to go through extra lengths to get this working.
> On a powermac is is certainly different.  You would have an apple
> partition table instead, along with whatever else a mac requires boot wise
> (which I don't know off hand).

So, MS-DOS partition tables will not work at all on a Mac, correct?


 .''`.  John Paul Adrian Glaubitz
: :' :  Debian Developer - address@hidden
`. `'   Freie Universitaet Berlin - address@hidden
  `-    GPG: 62FF 8A75 84E0 2956 9546  0006 7426 3B37 F5B5 F913

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